Phantom spiral aftereffect: Evidence for global mechanisms in perception

Abstract

The existence of phantom motion aftereffects (MAEs) makes it difficult to explain normal MAEs in terms of the activity of simple motion detectors. The alternative is to assume that MAEs are mediated by larger structures that respond more broadly to stimulus input. In this view, normal and phantom MAEs are manifestations of activation of a single structure and, therefore, should not differ in their qualitative and quantitative properties. This hypothesis was tested in two experiments, one that used experienced subjects and one that used naive subjects. The adapting stimulus was the upper half of a rotating spiral. Normal spiral aftereffects (SAEs) were observed over the upper half of a set of concentric circles; phanton SAEs were observed over the lower-half semicircles. Subjects continuously rated the strength of the aftereffect on an 11-point scale. The ratings were recorded every 5 sec. All subjects reported seeing normal and phantom SAEs in the appropriate respective directions. Rates of recovery from adaptation were remarkably similar. The results support the hypothesis that normal and phantom SAEs are a manifestation of activity in a structure larger than a simple motion detector. © 1984, The Psychonomic Society, Inc.. All rights reserved.